1. Field of the Invention
The invention relates to electro-optical data links generally, and more specifically to pulse laser responsers.
2. Description of the Prior Art
The most frequently used prior art data link devices are of the radio frequency type requiring a transmitter at the information site and usually arrange to broadcast a broad beam. Those particular facts make the information site vulnerable to detection and interception of the data, as well as subject to various countermeasures.
A particular class of devices which fits that description are the so-called radio and radar beacons (transponders). A specialized type of beacon within that general class of devices is so-called IFF transponder system. The general concept in connection with IFF (Identification Friend or Foe) is that a vehicle, usually an aircraft, approaching an aircraft carrier or other landing area, must be identified so that instructions may be given, or countermeasures initiated or withheld, as required, in the military situation. In civil aviation, this type of relatively automatic identification has applications also, in that the air space in the vicinity of air terminals, is frequently relatively crowded with aircraft of different types having different handling priorities and landing approach requirements.
Although security is a matter of less significance in connection with civil aviation than it is in military aviation, there are, nevertheless, many non-military situations in which the security (non-interceptibility and high immunity to countermeasures) is nevertheless desirable.
A background in radio and radar beacons may be obtained from Chapter 38 of the text "Radar Handbook" by Merrill Skolnik (McGraw-Hill 1970).
Laser communication and object detection systems are also known in the prior art. The particular virtues and special characteristics of coherent light beams (as used in laser equipment) has sparked the development of devices for generating and transmitting laser beams, for modulating and demodulating them, and for otherwise processing them. Certain elements and sub-combinations of the combination of the present invention are therefore known to those skilled in this art, per se, and these will be identified more specifically as this description proceeds.
The aforementioned radar handbook also includes a chapter on laser radars (Chapter 37). Therein, the prior art in respect to laser radars, is well summarized and a very extensive bibliography is appended thereto. Such aspects of the system of the present invention as laser beam tracking, detection and conversion to electrical signal form, as well as certain other known aspects of the instrumentation, are explained.